Unexamined Published Japanese Patent Applications (Kokai) Nos. 58-39551 and 63-64858 disclose known vehicle brake apparatus that include a brake pedal, a wheel cylinder, a pressure source and a master cylinder. When the pressure source is in the normal condition, the pressure source supplies hydraulic braking pressure to the wheel cylinder in response to operation of the brake pedal. On the other hand, if the pressure source cannot supply hydraulic braking pressure to the wheel cylinder, for example if the pressure source is broken, the master cylinder supplies hydraulic braking pressure to the wheel cylinder. These known apparatus are further defined by an electromagnetic valve which includes a solenoid. The electromagnetic valve is disposed between the master cylinder and the wheel cylinder. The electromagnetic valve is constructed to establish, when the solenoid is deenergized, communication between the master cylinder and the wheel cylinder. When the solenoid is energized, communication between the master cylinder and the wheel cylinder is prevented. As a result, when the pressure source supplies hydraulic braking pressure to the wheel cylinder, the solenoid of the electromagnetic valve is energized to cut off communication between the master cylinder and the wheel cylinder.
However, in the above-described brake apparatus, if the brake pedal is operated for a long period of time to maintain a standstill condition of the vehicle, the solenoid of the electromagnetic valve is also continuously energized for a long period of time. Thus, the electromagnetic valve must be constructed to handle the electricity and so the electromagnetic valve become expensive.
It is possible to address this drawback by constructing the electromagnetic valve so that communication between the master cylinder and the wheel cylinder is prevented when the solenoid is deenergized and to establish communication between the master cylinder and the wheel cylinder when the solenoid is energized. However, the disadvantage here is that communication between the master cylinder and the wheel cylinder cannot be established if the electromagnetic valve is broken and the master cylinder cannot supply hydraulic braking pressure to the wheel cylinder.
In light of the foregoing, a need exists for a vehicle brake apparatus that is not as susceptible to the same disadvantages and drawbacks as those described above.